When the regiment augmented the Hanoverian Army in 1760, the 8th King's had its grenadier company committed to the battles of Warburg and Kloster Kampen. As a complete regiment, the 8th served at Kirch-Denkern, Paderborn, Wilhelmsthal, and the capture of Cassel.
 

During its posting, the 8th King's possessed a number of officers adept in cultivating a relationship with tribes on the Great Lakes, the most notable being Captain Arent DePeyster and Lieutenant John Caldwell. Later to become 5th Baronet of County Fermanagh's Caldwell Castle, Caldwell immersed himself in his efforts to foster understanding between the British and Ojibwa, reputedly marrying a member of the tribe and becoming a chief under the adopted name of "The Runner".

In the west, Captain DePeyster's negotiations proved instrumental in maintaining peace between the British and tribes such as the Mohawk and Ojibwa nations. Born into a prominent New York family of Dutch origin, DePeyster held authority over Fort Michilimackinac. In 1778, using £19,000 of goods as leverage, he arranged for more than 550 warriors from several tribes to serve in Montreal and Ottawa.
 

Cedars

Detroit

Kentucky

Laurens

Michilimackinac

Newton

Niagara

Stanwix

Vincennes

Location of 8th Foot during the American Revolution

From Fort Oswegatchie, Captain George Forster of the regiment's light company led a composite force, including 40 regulars and about 200 warriors, across the St. Lawrence River to attack Fort Cedars, held by 400 Americans under Timothy Bedel. Forster maintained illicit contact with occupied Montreal, and received intelligence of American troop movements using Indian operatives and de Lorimier.

Arriving at the fort on 18 May, the British briefly exchanged fire before Forster parleyed with Bedel's successor, Major Isaac Butterfield, to request his surrender and warn him of consequences should Indian warriors be committed. The commander, whose men had been seemingly distressed by an earlier display of Indian war chanting, expressed a willingness to do so on the proviso of being allowed to retire with his weapons - a condition that Forster refused.

Emboldened by the two victories, the British landed at Pointe-Claire, on the Island of Montreal, but withdrew after Forster established the strength of General Benedict Arnold's force at Lachine. In pursuit of the dwindling column, Arnold pursued the British using bateaux but was deterred from landing by Forster's placement of men along the embankment at Quinze-Chênes, supported by two captured cannon pieces. Both Arnold and Forster postured, each threatening the other with the prospect of atrocities: the killing of prisoners by Forster's Indian allies and the destruction of Indian villages by Arnold's men. Having agreed favourable terms to a prisoner exchange with captives Butterfield and Shelburne, Forster's conditions were accepted by Arnold on 27 May, with the exception of Americans being forbidden from serving elsewhere. The decision would be denounced by the US Second Continental Congress and the arrangement reneged upon under the pretext that abuses had been committed by Forster's men.

In late July 1777, the regiment contributed Captain Richard Leroult and 100 men to the Siege of Fort Stanwix. Commanded by Lieutenant-Colonel Barry St. Leger, 34th Foot, the force consisted of approximately 1600 men, comprising British (100 8th, 100 34th) Canadian (65-100), German (350), Loyalist (400) and Native American (700) troops. At the Battle of Oriskany in August, Chief Joseph Brant's men and the King's Royal Regiment of New York intercepted American reinforcements for Stanwix, inflicting more than 400 casualties, including General Nicholas Herkimer. The fort itself was heavily defended and newly repaired and prepared for a siege, while the besiegers numbers were insufficient and their artillery of an inadequate calibree. During the time the ambush was taking place, a sortie by from the forts defenders swept out unopposed capturing much of the Loyalist and Indian camp and supplies. A few weeks later the siege collapsed with the disappearance of the dis-spirited native allies.

The regiment took part in further actions at Vincennes and the Battle of Newtown (Elmira, New York) in 1779, as well as the Mohawk Valley in 1780 and Kentucky in 1782. Captain Henry Bird of the 8th Regiment led a British and Native American siege of Fort Laurens in 1779. In 1780, he led an invasion of Kentucky, capturing two "stations" (fortified settlements) and returning to Detroit with 300 prisoners.